This invention relates to an injection molding method, and more particularly, to a method for continuously controlling the pressure of a gas preliminarily supplied to a mold cavity to thereby suitably maintain the temperature of the gas.
In the molding field, one of the most important requirements to obtain a high quality mold product resides in a temperature a difference, i.e. a difference in viscosities of a molten material, usually resin, at an injection starting point and at an injection completing point, and it is required to make small the viscosity difference of the molten resin at the injection starting and completing points.
With this in mind, in the well known art, the viscosity difference of the molten resin is made small generally by injecting the molten resin at considerably high speed into the mold cavity to shorten a time required for the injection. However, in this known technique, a hydraulic pump having a large capacity or a large sized accumulator to forcibly inject the molten resin into the mold cavity at a high speed is required. This unnecessarily enlarges the whole structure of an injection molding machine, and moreover, high speed injection may generally increase the occurrence of defective products with undesirable deformation and cracks. In addition, the high speed injection further requires a highly accurate response to the injection molding system such as for quickly switching the injection process from filling resin to holding a pressure, and such requirement of the high response to the injection molding control system includes various high leveled techniques and technical problems.